The main objective of the proposed project is to define the nature of trophic influences of motor neuron and its mechanism of action. Trophic influences are long-term interactions between the neuron and skeletal muscle tissue it innervates: these influences are responsible for the development and maintenance of the tissue. Recent evidence indicates that such trophic influences are independent of nerve transmission and are mediated by trophic substances released by nerve. We have isolated and partially purified a protein having neurotrophic properties from adult sciatic nerves. An in vitro bioassay system has been devised by which the trophic effects of peripheral nerve protein can be assayed. Assays include the effects of the protein on further differentiation and maturation of aneural embryonic muscle cells, induction or maintenance of the end-plate specific form of acetylcholinesterase of embryonic muscle and adult muscle in organ culture, and the synthesis and distribution of acetylcholine receptors on the surface of muscle in culture. Experiments are designed to isolate, further purify and characterize the protein which exerts neurotrophic influences on muscle from peripheral nerves. Rabbit antiserum to purified peripheral nerve protein will be produced and the immunoglobulin fraction is isolated. Using immunohistological procedures, the localization of the protein will be studied in motor nerve and at the neuromuscular junction. With immunoprecipitation techniques, the synthesis and possible migration (axonal transport) of the protein will be studied in motor nerve. The project will provide definitive evidence for the nature of trophic influences of motor neuron on muscles.